--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/spandsp-0.0.3/spandsp-0.0.3/src/spandsp/fsk.h	Fri Jun 25 16:00:21 2010 +0200
@@ -0,0 +1,242 @@
+/*
+ * SpanDSP - a series of DSP components for telephony
+ *
+ * fsk.h - FSK modem transmit and receive parts
+ *
+ * Written by Steve Underwood <steveu@coppice.org>
+ *
+ * Copyright (C) 2003 Steve Underwood
+ *
+ * All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2, as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ * $Id: fsk.h,v 1.17 2006/10/24 13:45:28 steveu Exp $
+ */
+
+/*! \file */
+
+/*! \page fsk_page FSK modems
+\section fsk_page_sec_1 What does it do?
+Most of the oldest telephony modems use incorent FSK modulation. This module can
+be used to implement both the trasmit and receive sides of a number of these
+modems. There are integrated definitions for: 
+
+ - V.21
+ - V.23
+ - Bell 103
+ - Bell 202
+ - Weitbrecht (Used for TDD - Telecoms Device for the Deaf)
+
+The audio output or input is a stream of 16 bit samples, at 8000 samples/second.
+The transmit and receive sides can be used independantly. 
+
+\section fsk_page_sec_2 The transmitter
+
+The FSK transmitter uses a DDS generator to synthesise the waveform. This
+naturally produces phase coherent transitions, as the phase update rate is
+switched, producing a clean spectrum. The symbols are not generally an integer
+number of samples long. However, the symbol time for the fastest data rate
+generally used (1200bps) is more than 7 samples long. The jitter resulting from
+switching at the nearest sample is, therefore, acceptable. No interpolation is
+used. 
+
+\section fsk_page_sec_3 The receiver
+
+The FSK receiver uses a quadrature correlation technique to demodulate the
+signal. Two DDS quadrature oscillators are used. The incoming signal is
+correlated with the oscillator signals over a period of one symbol. The
+oscillator giving the highest net correlation from its I and Q outputs is the
+one that matches the frequency being transmitted during the correlation
+interval. Because the transmission is totally asynchronous, the demodulation
+process must run sample by sample to find the symbol transitions. The
+correlation is performed on a sliding window basis, so the computational load of
+demodulating sample by sample is not great. 
+
+Two modes of symbol synchronisation are provided:
+
+    - In synchronous mode, symbol transitions are smoothed, to track their true
+      position in the prescence of high timing jitter. This provides the most
+      reliable symbol recovery in poor signal to noise conditions. However, it
+      takes a little time to settle, so it not really suitable for data streams
+      which must start up instantaneously (e.g. the TDD systems used by hearing
+      impaired people).
+
+    - In asynchronous mode each transition is taken at face value, with no temporal
+      smoothing. There is no settling time for this mode, but when the signal to
+      noise ratio is very poor it does not perform as well as the synchronous mode.
+*/
+
+#if !defined(_FSK_H_)
+#define _FSK_H_
+
+/*!
+    FSK modem specification. This defines the frequencies, signal levels and
+    baud rate (== bit rate for simple FSK) for a single channel of an FSK modem.
+*/
+typedef struct
+{
+    const char *name;
+    int freq_zero;
+    int freq_one;
+    int tx_level;
+    int min_level;
+    int baud_rate;
+} fsk_spec_t;
+
+/* Predefined FSK modem channels */
+enum
+{
+    FSK_V21CH1 = 0,
+    FSK_V21CH2,
+    FSK_V23CH1,
+    FSK_V23CH2,
+    FSK_BELL103CH1,
+    FSK_BELL103CH2,
+    FSK_BELL202,
+    FSK_WEITBRECHT,     /* Used for TDD (Telecom Device for the Deaf) */
+};
+
+extern fsk_spec_t preset_fsk_specs[];
+
+/*!
+    FSK modem transmit descriptor. This defines the state of a single working
+    instance of an FSK modem transmitter.
+*/
+typedef struct
+{
+    int baud_rate;
+    get_bit_func_t get_bit;
+    void *user_data;
+
+    int32_t phase_rates[2];
+    int scaling;
+    int32_t current_phase_rate;
+    uint32_t phase_acc;
+    int baud_frac;
+    int baud_inc;
+    int shutdown;
+} fsk_tx_state_t;
+
+/* The longest window will probably be 106 for 75 baud */
+#define FSK_MAX_WINDOW_LEN 128
+
+/*!
+    FSK modem receive descriptor. This defines the state of a single working
+    instance of an FSK modem receiver.
+*/
+typedef struct
+{
+    int baud_rate;
+    int sync_mode;
+    put_bit_func_t put_bit;
+    void *user_data;
+
+    int min_power;
+    power_meter_t power;
+    int carrier_present;
+    int16_t last_sample;
+
+    int32_t phase_rate[2];
+    uint32_t phase_acc[2];
+
+    int correlation_span;
+
+    int32_t window_i[2][FSK_MAX_WINDOW_LEN];
+    int32_t window_q[2][FSK_MAX_WINDOW_LEN];
+    int32_t dot_i[2];
+    int32_t dot_q[2];
+    int buf_ptr;
+
+    int baud_inc;
+    int baud_pll;
+    int lastbit;
+    int scaling_shift;
+} fsk_rx_state_t;
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/*! Initialise an FSK modem transmit context.
+    \brief Initialise an FSK modem transmit context.
+    \param s The modem context.
+    \param spec The specification of the modem tones and rate.
+    \param get_bit The callback routine used to get the data to be transmitted.
+    \param user_data An opaque pointer.
+    \return A pointer to the modem context, or NULL if there was a problem. */
+fsk_tx_state_t *fsk_tx_init(fsk_tx_state_t *s,
+                            fsk_spec_t *spec,
+                            get_bit_func_t get_bit,
+                            void *user_data);
+
+/*! Adjust an FSK modem transmit context's power output.
+    \brief Adjust an FSK modem transmit context's power output.
+    \param s The modem context.
+    \param power The power level, in dBm0 */
+void fsk_tx_power(fsk_tx_state_t *s, float power);
+
+void fsk_tx_set_get_bit(fsk_tx_state_t *s, get_bit_func_t get_bit, void *user_data);
+
+/*! Generate a block of FSK modem audio samples.
+    \brief Generate a block of FSK modem audio samples.
+    \param s The modem context.
+    \param amp The audio sample buffer.
+    \param len The number of samples to be generated.
+    \return The number of samples actually generated.
+*/
+int fsk_tx(fsk_tx_state_t *s, int16_t *amp, int len);
+
+/*! Get the current received signal power.
+    \param s The modem context.
+    \return The signal power, in dBm0. */
+float fsk_rx_signal_power(fsk_rx_state_t *s);
+
+/*! Adjust an FSK modem receive context's carrier detect power threshold.
+    \brief Adjust an FSK modem receive context's carrier detect power threshold.
+    \param s The modem context.
+    \param power The power level, in dBm0 */
+void fsk_rx_signal_cutoff(fsk_rx_state_t *s, float cutoff);
+
+/*! Initialise an FSK modem receive context.
+    \brief Initialise an FSK modem receive context.
+    \param s The modem context.
+    \param spec The specification of the modem tones and rate.
+    \param sync_mode TRUE for synchronous modem. FALSE for asynchronous mode.
+    \param put_bit The callback routine used to put the received data.
+    \param user_data An opaque pointer.
+    \return A pointer to the modem context, or NULL if there was a problem. */
+fsk_rx_state_t *fsk_rx_init(fsk_rx_state_t *s,
+                            fsk_spec_t *spec,
+                            int sync_mode,
+                            put_bit_func_t put_bit,
+                            void *user_data);
+
+/*! Process a block of received FSK modem audio samples.
+    \brief Process a block of received FSK modem audio samples.
+    \param s The modem context.
+    \param amp The audio sample buffer.
+    \param len The number of samples in the buffer.
+    \return The number of samples unprocessed.
+*/
+int fsk_rx(fsk_rx_state_t *s, const int16_t *amp, int len);
+
+void fsk_rx_set_put_bit(fsk_rx_state_t *s, put_bit_func_t put_bit, void *user_data);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
+/*- End of file ------------------------------------------------------------*/